With the increasing miniaturization of all types of electrical apparatus, operating switches for such apparatus must of necessity also be miniaturized. However, such switches must also be responsive to light operator pressure, have a mechanical switching action which has a good "feel" to the operator, and still provide reliable electrical operation.
In one form of conventional miniaturized push button switch, a see-saw contact mechanism is provided. More specifically referring to FIG. 1, a converter 25 is pivotably mounted within a switch body 20 by means of two support shafts 25a which project from opposite faces of converter 25 and which are mounted to corresponding inner surfaces of a cover 21 fixedly attached to the open top of switch body 20. An axially slidable push rod 23 having a button 30 on the free end thereof is mounted in a sleeve 22 which projects outwardly from cover 21. A rod-shaped actuator 24 having an enlarged head portion is interposed between push rod 23 and converter 25. The head portion of actuator 24 is inserted in a recess formed in the lower surface of push rod 23, as shown, and the main portion of actuator 24 extends through an orifice in cover 21 into an off-center recess formed in the upper surface of converter 25. A compression spring 27 is disposed around actuator 24 intermediate push rod 23 and switch cover 21. A plunger 29 and a compression spring 26 are disposed in a recess formed in the lower or bottom surface of converter 25 such that displacement of plunger 29 into the recess is resisted by spring 26. Three stationary contact members 10, 11 and 12 extend through the base of switch body 20 and a curvilinear movable contact member 28 is pivotally supported in a see-saw fashion on the central contact member 10 within the enclosure of switch body 20. The distal end of plunger 29 slidably engages the upper surface of movable contact member 28 and is displaceable along the length of contact member 28. As shown, the upper surface of contact member 28 slopes upwardly toward plunger 29 to provide an automatic restoring action to the switch.
In operation, when button 30 and thus push rod 23 is depressed in opposition to the force of spring 27, actuator 24 depresses the upper surface of converter 25, which causes converter 25 to be rotated counterclockwise about a pivot axis defined by shafts 25a. Plunger 29 is thus shifted toward contact 12, which causes spring 26 to be compressed. When the lower end of plunger 29 becomes aligned with central contact member 10, movable contact member 28 is rotated quickly clockwise in a see-saw fashion, thereby causing the connection between contacts 11 and 28 to be broken and the connection between contacts 12 and 28 to be closed. As the distal end of plunger 29 is displaced further up the slope of contact member 28, spring 26 is further compressed until reaching its state of maximum compression. When button 30 is released, the force of compressed spring 26 urges plunger 29 down the sloped surface of contact 28, causing converter 25 to be rotated clockwise, and push rod 23 to be pushed up by the force of spring 27, thereby restoring the switch to its original state.
The aforementioned prior art switch has several disadvantages. In addition to having a relatively complicated construction, both the force of spring 27 and the force of spring 26 must be opposed when button 30 is depressed. In addition, the force produced by spring 26 is accentuated because plunger 29 must travel up the sloped surface of contact 28. A large operating force is thus required. Furthermore, the operating force cannot be decreased by weakening the force of spring 26, since the contact pressure thus becomes weakened and the switch contact stability is decreased.